Liquid cooled rotor for dynamoelectric machines

ABSTRACT

A liquid cooled rotor for dynamoelectric machines in which a coolant liquid such as water circulates through passages in the rotor and is discharged through an axial bore and radial passages in the rotor shaft, and in which flow restricting arrangement are provided in the radial passages for controlling the flow of liquid due to the self-pumping action of the radial passages and for improving the pumping action, the flow restricting arrangement having a curved and convergent orifice which changes the direction of the discharged liquid from radial to a direction approaching the tangential and opposite to the direction of rotation of the rotor.

United States Patent [191 Curtis et a1.

[ June 19, 1973 22 Filed: Sept. 21, 1971 21 Appl. No.: 182,368

[5 6] References Cited UNITED STATES PATENTS 7/1963 Fechheimer 310/5410/1950 Fechheimer .1 310/54 3,476,961 11/1969 Heard .1 310/58 3,145,3148/1964 Becker.... 310/61 3,131,321 4/1964 Gibbs 310/64 PrimaryExaminer-R. Skudy Att0meyA. T. Stratton and F. P. Lyle [57] ABSTRACT Aliquid cooled rotor for dynamoelectric machines in which a coolantliquid such as water circulates through passages in the rotor and isdischarged through an axial bore and radial passages in the rotor shaft,and in which flow restricting arrangement are provided in the radialpassages for controlling the flow of liquid due to the self-pumpingaction of the radial passages and for improving the pumping action, theflow restricting arrangement having a curved and convergent orificewhich changes the direction of the discharged liquid from radial to adirection approaching the tangential and opposite to the direction ofrotation of the rotor.

6 Claims, 3 Drawing Figures Patented June 19, 1973 3,740,596

3 Sheets-Sheet 2 Patented Junel9, 1973 3,740,596

3 Shoots-Sheet 5 FIG. 3

LIQUID COOLED ROTOR FOR DYNAMOELECTRIC MACHINES BACKGROUND OF THElNVENTlON ant fluid is circulated through duct means in the stator androtor slots in direct thermal relation with the current-carryingconductors inside the ground insulation. This type of constructionprovides a very effective cooling system, and has made it possible togreatly increase the maximum ratings obtainable in large generatorswithout exceeding the permissible limits of physical size. The coolantused in these machines has usually been hydrogen, which fills thegas-tight housing and is circulated by a blower on the rotor shaftthrough the ducts of the stator and rotor windings and through ducts inthe stator core.

The maximum ratings required in large generators have continued toincrease, however, making it necessary to further improve the cooling ofthese machines in the largest sizes. A substantial improvement incooling can be obtained by the use of more efficient coolant fluids suchas liquids. This has been done in stators by circulating a liquidcoolantsuch as water through the ducts of the stator winding, and aconsiderable improvement in cooling has thus-been obtained. Asubstantial further improvement can be obtained by applying liquidcooling to the rotor by circulation of a suitable liquid such as waterthrough passages in the rotor windings.

Many problems are involved, however, in circulating a liquid coolantthrough the rotor of a large generator. In one desirable type ofconstruction, the water or other coolant liquid is introduced into therotor along the axis of the shaft at one end and flows through an axialpassage and radial passages to an annular distributionchamber on thesurface of the rotor, from which the liquid is distributed toindividualconductors of the rotor winding-. The liquid flows through passages inthe winding conductors and at the other end flows to an anv nularcollecting chamber on the rotor surface. The liquid is discharged fromthe collecting chamber through radial passages to an axial bore at thecenter of the shaft, and flows axially through the bore to another setof radial passagesjthrough which it is discharged from the rotor toafstationary discharge chamber.

The radial discharge passages act as a centrifugal pump, and'provide astrong self-pumping action. The minimum diameter of these passages isdetermined primarily by the necessity for access to their radially innerends for welding stainless steel liners to a stainless steel liner inthe shaft bore with which the passages communicate. This requirementsets a minimum diameter sufficiently large to make it necessary torestrict the flow of water .throughthe radial passages, both to controlthe flow rate through the rotor due to the self-pumping action and tomaintain a static pressure high enough to prevent cavitation. It hasbeen proposed to restrict the flow of liquid in rotors of this type bymeans of simple orifices disposed in the radial passages, as inFechheimer U.S. Pat. No. 2,527,878 and l-leard et al. U.S. Pat. No.3,398,304. It has been found by test, however,

' that such orifices do not give satisfactory results, and

severe vibration of the stationary discharge chamber can also occurbecause of the large impact forces of the high velocity flow from therotor passages.

SUMMARY OF THE lNVENTlON In accordance with the present invention,improved means are provided for restricting the flow of liquid throughthe radial discharge passages of a liquid cooled rotor of the generaltype described above. More specifically, each of the radial passages isclosed by a plug member secured in the outer end of the passage adjacentthe surface of the rotor, and the plug member has a discharge opening ororifice extending through it for flow of liquid discharged through theradial passage. The orifice restricts the flow of liquid and changes itsdirection, being substantially radial at the inner or entrance end, andchanging to a more nearly tangential direction at the outer or dischargeend, so that the liquid is discharged in a direction approaching thetangential and opposite to the direction of rotation of the rotor. Theorifice decreasesin diameter from the inner end to the outer end so asto gradually converge towards the discharge end to restrict theflowthrough the orifice. The change in direction of the liquid dischargedfrom the rotor has a very important effect on the pumping action, andincreases the hydraulic efficiency so that the pumping power requiredfor a given flow rate is greatly decreased. The change in direction ofHow from radial to a more nearly tangential direction opposite to thedirection of rotation also eliminates the problem of vibration of thedischarge chamber. The gradually converging discharge channel minimizeslosses in the flow through the orifice and thus further contributes tothe overall efficiency of the design.

BRIEF DESCRIPTION 0F THE DRAWINGS The invention will be more fullyunderstood from the following detailed description of an illustrativeembodiment, taken in connection with the accompanying drawings, inwhich:

FIG. 1 is a view in longitudinal section and partly in elevation of aturbine generator, having a liquid cooled rotor embodying the invention;

FIG. 2 is a fragmentary longitudinal sectional view at the discharge endof the rotor shaft showing one of the discharge passages; and

FIG. 3 is a fragmentary transverse sectional view substantially on theline Ill-lIl of FIG. 2, but showing the full rotor shaft.

DESCRIPTION OF THE PREFERRED EMBODlMENT Referring first to FIG. 1 of thedrawing, the invention is shown embodied in the rotor ofa large turbinegenerator of typical construction, although it will be understood thatthe rotor of the present invention may be used in machines of anydesired type. As shown, the generator has a stator core 10, supported byframe rings 12 in a substantially gas-tight outer housing 14. The statorcore 10 is of the usual laminated construction, having a generallycylindrical bore therethrough, and the laminations are clamped betweensuitable end plates 15 in the usual manner. The stator core 10 haslongitudinal slots in its inner periphery for the reception of a statorwinding 16, which may be of any suitable type but which is shown as aliquid cooled winding.

For this purpose, circular inlet and discharge manifolds 17 are providedat opposite ends of the machine and connected through suitable means,generally indicated at 18, to circulate a coolant liquid such as waterthrough the coils of the stator winding 16. The manifolds 17 may beconnected as indicated diagramatically at 19 to an externalrecirculating system of any desired type. The housing 14 is filled witha coolant gas, preferably hydrogen, which is circulated through theinterior of the housing to cool the stator core by flowing throughcooling ducts, and suitable baffling of any desired type may be providedin the housing to direct the flow of gas therein.

The machine has a rotor member 20, which is disposed in the bore of thestator core and supported in bearings 21 in the ends of the housing 14.The bearing assemblies preferably include gland seals to prevent leakageof gas along the rotor shaft, and may be of any suitable or usualconstruction but have not been illustrated in detail as they are not apart of the invention. The rotor member 20 has a central body portion 25which is provided with peripheral slots in the usual manner for thereception of a rotor winding 26. The winding 26, which constitutes thefield winding of the generator, may be arranged in any suitable mannerin the slots of the rotor to form the desired number of magnetic poles,usually either two or four in machines of this type. The winding 26 isconstituted of copper conductors whichv extend longitudinally throughthe slots of the rotor body 25 and generally circumferentially in theend turn portions 28, which lie beyond the ends of the body portion 25and are supported against rotational forces by the usual heavy retainingrings 29. The conductors of the rotor winding are hollow or have centralpassages extending through them for flow of coolant liquid from one endof the winding to the other. Any suitable or desired type of flowpattern may be utilized, and any desired type of electrical circuit maybe used.

The rotor 20 shown in the drawing is a liquid cooled rotor of theconstruction more fully disclosed and claimed in a copending applicationof L. P. Curtis et al., Ser. No. 144,050, filed May 17, 1971 andassigned to the assignee of the present invention. The rotor 20 hasshaft portions 30 extending axially from each end of the body portion 25and preferably integral therewith. The rotor has a central axial bore 31which, in accordance with usual practice,,may extend for the entirelength of the rotor'from one end to the other. As more fully describedin the above-mentioned copending application, a coolant liquid,preferably water, is introduced through the shaft portion 30 at theleft-hand end, as viewed'in the drawing, and flows through an annularpassage 32 in the bore 31. The passage 32 is preferably formed by twoconcentric stainless steel tubes and surrounds axial electrical leads33, which provide electrical connectionto the rotor winding 26. Thewater flows through the passage 32 to opposed radial passages 34, whichextend to an annular distribution chamber 35 on the surface of the rotorshaft 30. Water is distributed I from the annular chamber 35- by meansof hydraulic connectors 36 of any suitable type to the individualconductors of the rotor winding, the connections being made to' the endturns 28.

The water flows through the hollow conductors of the rotor winding tothe other end, and is discharged through similar connectors 37 to anannular collecting chamber 38 on the shaft 30 at the right-hand end ofthe rotor. The water flows from the chamber 38 through two opposedradial passages 39 to the bore 31 of the shaft and axially through thebore 31 to opposed radial passages 40 which extend to the surface of therotor shaft 30. The water is discharged through these passages 40 into astationary discharge chamber 41 which is provided with suitable seals toprevent escape of the water, and the water is discharged through a drain42, preferably to be treated and recirculated in a closed system.

All passages and surfaces exposed to the coolant are preferably lined orcovered with stainless steel, or other corrosion resistant material, toprevent corrosion of the rotor steel by the heated coolant water. Inparticular, at the discharge end of the rotor, the axial bore 31 islined with a stainless steel tubular liner 44, which extends between thetwo sets of radial passages 39 and 40 and which is closed at each end bya plate or plug 45 of any suitable type welded or otherwise secured inthe ends of the liner 44 with a liquid-tight joint. The passages 39 and40 are similarly lined with tubular stainless steel liners 46 welded orotherwise sealed to the tubular liner 44 of the shaft bore. Any othersuitable corrosion resistant material might of course be utilizedinstead of stainless steel if desired.

As previously discussed, the opposed radial discharge passages 40function as a centrifugal pump and provide a strong self-pumping actionon the water flowing through the rotor. The necessity of obtainingaccess to the inner end of the passages 40 for welding the liners 46 tothe bore liner 44 sets a minimum diameter for the passages 40 which issufficiently large to make it necessary to restrict the flow of liquidthrough the passages 40. This restriction is necessary to control thewater flow to a desired flow rate and also to maintain the pressure inthe passages above the cavitation pressure. It is necessary therefore toprovide flow restricting means in the passages 40. Simple orifice platesmight be utilized for this purpose, but it has been found by test thatsuch plates are not satisfactory as they greatly reduce the efficiencyof the pumping action and also cause severe vibration of the stationarydischarge chamber 41 because of the large impact forces resulting fromthe large velocity components of the radial discharge.

In accordance with the present invention, a flow restrictor is providedin each passage which has a curved discharge channel or orificetherethrough which changes the direction of the water from radial to adirection approaching tangential in the direction opposite to thedirection of rotation of the rotor. The discharge channel is ofgradually reducing diameter from the entrance end to the discharge endto provide a converging flow channel for smooth transition andrestriction of flow with minimum loss. In the preferred embodiment shownin the drawing the flow restrictor consists of a plug 48 of stainlesssteel or other corrosion resistant material threaded in each of thepassages 40 at the outer end adjacent the surface of the rotor shaft 30.Each plug 48 has an orifice or discharge channel 49 extending through itfor discharge of water flowing in the radial passage 40. As clearlyshown in FIG. 3, the discharge orifice 49 is generally radial at theinner or entrance end but is curved to change direction as it passesthrough the plug 48 so that its outer or discharge end 50 discharges theliquid in a direction which approaches the tangential, and which isopposite to the direction of rotation of the rotor indicated by thearrow in FIG. 3. It will also be seen that the discharge channel 49 isof relatively large diameter at its entrance end and gradually decreasedin diameter, or cross sectional area, towards the discharge end, so asto provide a gradually converging water channel leading to a relativelysmall discharge opening 50. If desired, a vent tube 51 for venting airor other gas from the region of the rotor axis may also extend throughthe plug 48, and is preferably attached to a support member 52 securedto the plug 48, as more fully disclosed and claimed in a copendingapplication of PR. Heller et al., Ser. No. 182,367, filed Sept. 21,1971, and assigned to the assignee of the present invention.

The curved and convergent discharge orifice 49 provides greatly improvedresults, as compared to a simple orifice plate. As previously stated, ifthe water is discharged radially from the rotor, through a dischargeorifice or otherwise, the pumping power required is high and excessivevibration occurs in the stationary discharge chamber 41 into which thewater is discharged. It has been found that as the direction ofdischarge of the water changes from the radial direction to a directionapproaching the tangential, the power required for pumping changescorrespondingly and is greatly reduced. That is, the pumping powervaries markedly with the discharge angle of the water, which may bedefined as the angle between the direction of the discharged waterrelative to the rotor and a tangent to the surface of the rotor at thepoint of discharge. For example, it has been found by test that when thedischarge angle is decreased from 90, which would be radial, to a smallangle such as shown in FIG. 3, the pumping torque required is decreasedby about 75 percent. In one particular embodiment, involving a 21 inchdiameter shaft with radial passages 40 having a length of 10.5 inchesand with a flow of 400 gallons per minute of water at 3,600 rpm, thepumping power required was decreased by about 200 KW as the dischargeangle of the water was changed from substantially radial to the angleshown in FIG. 3. It will be obvious that this is a very significantimprovement. The gradually convergent discharge channel 49 is alsoimportant to the improved performance since the gradual convergenceeffects the desired restriction of flow with minimum friction and eddylosses. The gradually reducing area of the curved flow channel 49, asillustrated in FIGS. 2 and 3, results in a transition of the flow fromradial to a nearly tangential direction, and in the desired restrictionof flow, with a smooth conversion of pressure head to velocity withrelatively small losses, so that the overall efficiency is furtherimproved by this action. Furthermore, the change in direction of thedischarged water and the reduction in the absolute velocity, as comparedto a radial discharge, results in the complete elimination of anyvibration of the discharge chamber 41.

It will now be apparent that a flow restrictor has been provided for aliquid cooled rotor which is very effective in controlling the flow ofliquid through radial discharge passages in a manner which greatlyimproves the hydraulic efficiency of the structure, and which minimizeslosses in the flow channel, as well as eliminating any vibration problemin the stationary discharge chamber. A particular embodiment of theinvention has been shown and described for the purpose of illustration,but it will be apparent that other embodiments and modifications arepossible, and all such embodiments are within the scope of theinvention.

We claim:

1. In a rotor member for a dynamoelectric machine, said rotor memberhaving passages for circulation of a liquid coolant therethrough, saidpassages including an axial passage and opposed radial passagescommunicating with the axial passage and extending to the surface of therotor for discharging liquid therefrom, and means in each of said radialpassages for restricting the flow of liquid therethrough and dischargingthe liquid in a non-radial direction approaching the tangential andopposite to the direction of rotation of the rotor.

2. The combination defined in claim 1 in which the restricting means hasa curved discharge passage which converges in size toward the dischargeexit.

3. The combination defined in claim 1 in which said flow restrictingmeans comprises a plug member secured in each radial passage adjacentthe surface of the rotor, each plug member having an orifice extendingtherethrough adapted to restrict the fiow of liquid and to change itsdirection.

4. The combination defined in claim 3 in which said orifice is a curvedpassage which changes direction from substantially radial at theentrance to a direction approaching the tangential at the dischargeexit.

5. The combination defined in claim 3 in which said orifice converges inarea toward the discharge exit.

6. The combination defined in claim 4 in which said orifice decreases indiameter from the entrance end to the discharge exit.

1. In a rotor member for a dynamoelectric machine, said rotor memberhaving passages for circulation of a liquid coolant therethrough, saidpassages including an axial passage and opposed radial passagescommunicating with the axial passage and extending to the surface of therotor for discharging liquid therefrom, and means in each of said radialpassages for restricting the flow of liquid therethrough and dischargingthe liquid in a non-radial direction approaching the tangential andopposite to the direction of rotation of the rotor.
 2. The combinationdefined in claim 1 in which the restricting means has a curved dischargepassage which converges in size toward the discharge exit.
 3. Thecombination defined in claim 1 in which said flow restricting meanscomprises a plug member secured in each radial passage adjacent thesurface of the rotor, each plug member having an orifice extendingtherethrough adapted to restrict the flow of liquid and to change itsdirection.
 4. The combination defined in claim 3 in which said orificeis a curved passage which changes direction from substantially radial atthe entrance to a direction approaching the tangential at the dischargeexit.
 5. The combination defined in claim 3 in which said orificeconverges in area toward the discharge exit.
 6. The combination definedin claim 4 in which said orifice decreases in diameter from the entranceend to the discharge exit.